The present invention pertains generally to optical switches. More particularly, the present invention pertains to optical switches that selectively route light beams on paths through free space. The present invention is particularly, but not exclusively, useful as an optical switch for operationally selecting a particular free-space light beam path from a plurality of possible beam paths.
The transmission of data over a fiber optic telecommunications system has many advantages. For one, the data transmission is accomplished at the speed of light. Further, fiber optic systems are known to provide high potential bandwidths, and they generally involve lower costs than the more traditional use of copper. Nevertheless, despite these advantages, there are some significant design considerations to be confronted when fiber optics are to be used in a telecommunications system.
A very important design consideration for the manufacture and operation of a fiber optic telecommunications system involves the optical fiber itself. In general, optical fibers are constructed with a central core and a cladding that surrounds the core. More specifically, optical fibers are typically made of ultra-pure glass wherein the central core is of a higher refractive-index than the outer cladding. With this structure, it is well known that an optical fiber is capable of conducting modulated light signals by total internal reflections of the signals inside the core. Presently, fiber optic communications systems are in use that incorporate such fibers either individually, or as cables which include groups of fibers. In either case, one major advantage for using optical fibers in a telecommunications system is the fact that they typically have very small diameters and, therefore, they can be engineered to occupy minimal space.
In many communications applications, it happens that a data transmission circuit needs to be rerouted or reconfigured in some way. For the specific case where optical fibers are being used for the construction of the circuit, such a rerouting requires that the modulated light signals being carried on one optical fiber need to somehow be transferred to another optical fiber. Such a transfer effectively requires the light signals that emanate from an end of one optical fiber be effectively directed onto the end of another optical fiber. More specifically, this requires the light signals be directed into the core of the receiving optical fiber. On this point, the size advantage that was mentioned above, raises other issues. In perspective, the difficulty here becomes more apparent when one considers that the typical optical fiber has a core diameter of about nine microns (9 xcexcm). Further, the total diameter of an optical fiber, for both the core and the cladding, is only about one hundred and twenty five microns (125 xcexcm). For an efficient communication system it is necessary to direct a light beam into the core of the optical fiber with what is commonly referred to as xe2x80x9cminimal insertion loss.xe2x80x9d To do this, most, if not all, of the light beam needs to be directed into the core of the optical fiber (i.e. onto a target of approximately 9 xcexcm diameter).
In light of the above, it is an object of the present invention to provide a photonic switch that minimizes the insertion loss when the light signals in a data communications beam are transferred from one optical fiber to another optical fiber. Another object of the present invention is to provide a photonic switch wherein the input aperture from one optical fiber in the switch is substantially on the same surface as the output aperture into another optical fiber in the switch. Still another object of the present invention is to provide a photonic switch that allows the effective transfer of light signals emanating from one optical fiber, to be selectively directed to a particular receiving optical fiber, wherein the receiving optical fiber is one in a plurality of receiving optical fibers. Yet another object of the present invention is to provide a photonic switch that is simple to use, relatively easy to manufacture and comparatively cost effective.
A photonic switch in accordance with the present invention includes a beam steering mirror which is positioned to interact with a plurality of waveguides. Preferably, each individual waveguide is an optical fiber and the beam steering mirror is movable to selectively direct a light beam through free-space from one optical fiber to another for the purpose of completing an optical circuit.
For the photonic switch of the present invention, the waveguides are mounted together in a substantially planar array. More specifically, an end of each waveguide (optical fiber) is positioned in the planar array. Also, at least one of the waveguides, preferably one near the center of the array, is positioned to transmit a light beam through free space toward the mirror. The mirror then reflects the light beam from the mirror, back toward the array. Additionally, a mechanism is provided which can move the beam steering mirror so that the reflected light beam is directed to a particular waveguide (optical fiber) in the array. Thus, an optical connection can be made between the transmitting waveguide and the particular receiving waveguide in the array.
For one embodiment of the present invention, the beam steering mirror is substantially flat. For this embodiment, the beam steering mirror is located substantially at the telecentric stop of a collimating lens that is positioned between the mirror and the planar array of waveguides. Thus, the light beam passes through the collimating lens en route to the mirror from a transmitting waveguide in the planar array. The light beam is then reflected by the mirror back through the collimating lens toward the selected waveguide. For another embodiment, the beam steering mirror can have a concave (e.g. spherical) surface. For this embodiment, the array can have a compatible concave surface or be optically altered to minimize such a surface. In both embodiments, the mirror functions to complete an optical circuit by directing a light beam from one waveguide (optical fiber) in the array, to another waveguide (optical fiber) in the array with minimal insertion loss.
The mechanism mentioned above for moving the mirror needs to be capable of providing for specific movements of the mirror. Specifically, consider the mirror defines an x-y-z coordinate system. Then, for both embodiments of the present invention (i.e. the mirror is flat or concave), the mirror needs to be moveable in rotation through an angle xcex8 around the x-axis with a range of approximately xc2x110xc2x0, and in rotation through an angle xcfx86 around the y-axis with a range of approximately xc2x110xc2x0. For purposes of the present invention, these movements can be accomplished by any mechanism known in the pertinent art. For example, such mechanisms for moving mirrors include magnetic actuators, mechanical actuators, piezo-electrical actuators and electrostatic and magnetic MEMS (Micro Electro Mechanical Systems). Further, for the embodiment of the present invention wherein the mirror has a concave surface, the mirror may need to be moveable along the z-axis.